Over the past two years, progress in X-ray crystallography, NMR spectr
oscopy and electron microscopy has begun to reveal the complex structu
re of the RNA within the ribosome. The structures of ribosomal protein
s L11 and S15, among others, show how RNA-protein interactions organiz
e the conformation of the junctions between ribosomal RNA helices. Gen
etic and biochemical methods have also identified a three base-pair sw
itch within the 16S rRNA that is linked to mRNA decoding.